Characterization of meteorological drought using SPI and SPEI indices in Kaduna State, Nigeria

Meteorological droughts pose a persistent threat to rainfed agriculture in Kaduna State, Nigeria. This study aimed to examine meteorological drought in Kaduna State, Nigeria, from 1981 to 2024 using the Standardized Precipitation Index (SPI) and Standardized Precipitation Evapotranspiration Index (SPEI) at time scales of 3, 6, 9, 12, and 24 months, with trends assessed using the Mann–Kendall test, and the indices compared using the Pearson correlation, mean difference, Root Mean Square Error, Mean Absolute Error (MAE), and Kling-Gupta Efficiency (KGE). The results revealed that SPI and SPEI detected drought events, and their duration and severity increased over longer timescales. SPI-3 detected the most intense drought (−4.317), while the most severe SPEI-3 drought had a magnitude of −3.355. The SPI-24 detected a 26-month drought with a highest severity of −3.351, while SPEI-24 detected a 35-month drought event between 1983 and 1986. SPI showed significant wetting trends at 12- and 24-month scales (p < 0.05), SPEI exhibited no significant trend at any timescale. Results of the comparison between SPI and SPEI revealed a strong positive correlation, particularly for the 6-month timescale (r > 0.94), but diverged at short and long timescales, most likely due to temperature influence. The study concluded that the difference between SPI and SPEI may be attributed to the influence of warming temperatures on atmospheric demand. The masking of precipitation gains by temperature-induced evaporation represents a common but under-recognized climate-change impact across Savanna and semi-arid regions globally, emphasizing the need to prioritize SPEI over precipitation-only indices for drought monitoring and adaptation planning.